a) Field of the Invention
The present invention relates to a method of forming a flat wiring layer with a damascene method, and more particularly to a flat wiring layer forming method capable of forming a low resistance and high reliability flat wiring layer by depositing a conductive layer inlaid in connection holes and interconnect grooves formed in an insulating film and thereafter planarizing the conductive layer.
b) Description of the Related Art
A flat wiring layer forming method with a damascene method is already known, for example, as illustrated in FIGS. 28 to 30 (e.g., refer to "DUAL DAMASCENE: A ULSI WIRING TECHNOLOGY", Carter W. Kaanta et al. Jun. 11-12, 1991 VMIC Conference).
At the process shown in FIG. 28, after wirings 2A and 2B are embedded in a surface layer of an insulating film 1, the surface of the insulating film 1 is planarized by CMP (chemical mechanical polishing). Another insulating film 3 is formed on the planarized surface of the insulating film 1.
A resist pattern 4 having holes 4a and 4b corresponding to connection portions to the wirings 2A and 2B is formed on the insulating film 3. Another resist pattern 5 is formed on the resist pattern 4, the resist pattern 5 having an interconnect hole coupling the holes 4a and 4b of the resist pattern 4.
In the process shown in FIG. 29, by using the resist patterns 4 and 5 as a mask, the insulating film 3 is dry-etched to form connection holes 3a and 3b reaching the wirings 2A and 2B and an interconnect groove 3A coupling the connection holes 3a and 3b, respectively in the insulating film 3. The connection holes 3a and 3b correspond to the holes 4a and 4b of the resist pattern 4, and the interconnect groove 3A corresponds to the hole 5A of the resist pattern 5.
At the process shown in FIG. 30, a W (tungsten) layer 6 is deposited on the insulating film 3 by CVD (chemical vapor deposition), the W layer 6 filling the connection holes 3a and 3b and interconnect groove 3A. The W layer 6 is planarized by CMP to leave a portion of the W layer 6 in the connection holes 3a and 3b and interconnect groove 3A.
With this conventional technique, the material of the wiring 6A is tungsten having a high resistivity so that a wiring resistance becomes high.